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Speech Production and Perception
Published in Philipos C. Loizou, Speech Enhancement, 2013
Stops are subclassified into voiceless (/p, t, k/) and voiced (/b, d, g/). Voiced stops differ from unvoiced ones in the characteristics of their closure and duration. In unvoiced stops, there is no flow of air out of the vocal tract during the closure. In voiced stops, a low-intensity periodic signal (at the fundamental frequency) may pass through during all or part of the duration of the closure. This low-intensity periodic signal is called the voice bar and appears as a constant low-frequency signal on the spectrogram (see Figure 3.14b). Voiced stops are on average shorter in duration than voiceless ones. The voiced onset time (VOT), that is, the time interval between the release of the burst and the onset of vocal fold vibrations, is about 10–20 ms for the voiced stops and 40–100 ms for the unvoiced ones [16]. Finally, the release burst, which shows in spectrograms as a vertical stripe following the silent gap (closure), is more intense in the voiceless stops than in the voiced ones (see example in Figure 3.14).
Acoustic–Phonetic Analysis for Speech Recognition: A Review
Published in IETE Technical Review, 2018
Biswajit Dev Sarma, S. R. Mahadeva Prasanna
During the production of stops and affricates, the vocal tract is completely closed creating a pressure build-up behind the closure. Closing the vocal tract creates silent interval for unvoiced sounds and a low-level signal for voiced sounds. When the pressure is released suddenly, a relatively high-energy transient or burst appears in the acoustic signal. The time interval between the onset of burst and the onset of voiced region in a stop consonant unit is known as voice onset time (VOT) [2]. In unvoiced sounds, a burst occurs before the onset of voiced region and hence, VOT is a positive value. On the other hand, in voiced sounds, onset of voiced region occurs prior to burst, hence VOT is negative. A positive VOT is called as VOT lag and a negative VOT is known as VOT lead.